Block copolymer rubber, resin modifier, and resin composition

ABSTRACT

An aromatic vinyl-conjugated diene block copolymer rubber comprising 50 to 75% by weight of conjugated diene monomer units and 25 to 50% by weight of aromatic vinyl monomer units, wherein the content of vinyl bond in the conjugated diene monomer units is at least 50% by weight, the ratio of blocked aromatic vinyl in the aromatic vinyl monomer units is at least 70% and the number average molecular weight of the copolymer rubber is in the range of 280,000 to 1,000,000. An aromatic vinyl resin having incorporated therein the aromatic vinyl-conjugated dione block copolymer rubber gives a shaped article having good impact resistance and luster, and characterized in that the luster is thermally stable and the luster varies only to a minimized extent within the shaped article.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP01/01341 which has an Internationalfiling date of Feb. 23, 2001, which designated the United States ofAmerica.

TECHNICAL FIELD

This invention relates to a novel block copolymer rubber, a modifier forresin comprising the block copolymer rubber as an effective ingredient,a resin composition comprising the modifier for resin, and a process forproducing the resin composition.

BACKGROUND ART

High-impact polystyrene resin (HIPS) is a modified polystyrene resinprepared by incorporating a polymer rubber such as a conjugated dienecopolymer rubber as a modifier for resin in a polystyrene resin havingpoor impact resistance to remedy this deficiency. HIPS has good impactresistance, rigidity and processability and therefore it is widely usedfor electric appliances, business machines, packaging containers,miscellaneous goods and other articles.

In general, when a rubbery modifier for resin is incorporated inpolystyrene resin, luster inherently possessed by the polystyrene resintends to be deteriorated. To minimize deterioration of luster, someproposals have been made. For example, Japanese Examined PatentPublication (JP-B) No. S48-18594 (GB 1,230,507) discloses a method usinga modifier for resin, comprising a butadiene-styrene block copolymercontaining butadiene units having a vinyl bond content of 5 to 25% byweight. However, a resin composition made by using this modifier has aproblem such that the deterioration of luster cannot be reduced to thedesired extent and the luster varies within a shaped article. JP-BS60-57443 (U.S. Pat. No. 4,282,334) discloses a process for producing animpact-resistant polystyrene resin by a specific polymerizationprocedure using a butadiene-styrene block copolymer containing 20 to 55%by weight of styrene as a rubbery modifier. However, a resin compositionobtained by this process has a problem such that the impact resistanceis insufficient and, when the resin composition is injection-molded, theluster of the resulting molded article varies within the molded article.

Japanese Unexamined Patent Publication (JP-A) No. H6-220141 discloses amethod using a modifier for resin, comprising an aromaticvinyl-conjugated diene block copolymer rubber having a vinyl bondcontent of at least 40% in the conjugated diene units and a molecularweight of 30,000 to 250,000. JP-A S57-30712 and JP-A S57-30714 disclosea method using a modifier for resin, comprising a styrene-butadienerandom copolymer having a styrene content of 3 to 30% by weight and avinyl bond content of at least 60% in the butadiene units. However, theformer method has a problem such that the impact resistance of theresulting resin composition is insufficient and the luster thereof isgreatly reduced. The latter method has a problem such that, when theresin composition is injection-molded, the luster of the resultingmolded article is insufficient and greatly varies within the moldedarticle, and, when a heat load is imposed on the molded article, theluster is greatly reduced.

DISCLOSURE OF THE INVENTION

A primary object of the present invention is to provide animpact-resistant aromatic vinyl resin composition having good impactresistance and luster and especially characterized in that the luster isreduced only to a minor extent even in a high-temperature environmentand varies to a minimized extent within a shaped article.

Another object of the present invention is to provide a modifier forresin, used for the production of the above-mentioned impact-resistantaromatic vinyl resin composition.

To achieve the above-mentioned objects, the present inventors madeextensive researches, and found that a modifier for resin, comprising anaromatic vinyl-conjugated diene block copolymer rubber having a highvinyl bond content in the conjugated diene monomer units, comprising aspecific amount of aromatic vinyl monomer units with a high blockedratio, and having a specific number average molecular weight gives aresin composition having a well-balanced luster and impact resistance,and further found that the aromatic vinyl-conjugated diene blockcopolymer rubber is not described in a literature and is novel. Based onthese findings, the present invention has been completed.

Thus, in a first aspect of the present invention, there is provided anaromatic vinyl-conjugated diene block copolymer rubber comprising 50 to75% by weight of conjugated diene monomer units and 25 to 50% by weightof aromatic vinyl monomer units, wherein the content of vinyl bond inthe conjugated diene monomer units is at least 50% by weight, the ratioof blocked aromatic vinyl is at least 70% and the number averagemolecular weight of the copolymer rubber is in the range of 280,000 to1,000,000.

In a second aspect of the present invention, there is provided amodifier for resin which comprises the above-mentioned block copolymerrubber as an effective ingredient.

In a third aspect of the present invention, there is provided a resincomposition comprising 2 to 25% by weight of the above-mentioned blockcopolymer rubber and 98 to 75% by weight of a resin.

In a fourth aspect of the present invention, there is provided a processfor producing a resin composition comprising polymerizing a monomer forforming a resin in the presence of the above-mentioned block copolymerrubber.

BEST MODE FOR CARRYING OUT THE INVENTION

[Block Copolymer Rubber]

The block copolymer rubber of the present invention comprises 50 to 75%by weight of conjugated diene monomer units and 25 to 50% by weight ofaromatic vinyl monomer units, wherein the content of a vinyl bond in theconjugated diene monomer units is at least 50% by weight, the ratio ofblocked aromatic vinyl is at least 70% and the number average molecularweight of the block copolymer rubber is in the range of 280,000 to1,000,000.

Conjugated diene monomers used for the production of the above-mentionedblock copolymer rubber are not particularly limited, and include, forexample, 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene),2,3-dimethyl-1,3-butadiene and 1,3-pentadiene. These conjugated dienemonomers may be used either alone or as a combination of at least twothereof. Of these, 1,3-butadiene and2-methyl-1,3-butadiene arepreferable. 1,3-butadiene is especially preferable.

The content of the conjugated diene monomer units in the block copolymerrubber is such that the lower limit thereof is 50% by weight andpreferably 55% by weight, and the upper limit thereof is 75%, preferably73% by weight and more preferably 65% by weight. When the content of theconjugated diene monomer units is too small, the luster becomes poor. Incontrast, when the content of the conjugated diene monomer units is toolarge, the impact resistance becomes poor.

The content of vinyl bond in the conjugated diene monomer units is suchthat the lower limit thereof is 50% by weight and preferably 55% byweight, and the upper limit thereof is preferably 90% by weight and morepreferably 80% by weight. When the vinyl bond content is too small, theluster tends to be deteriorated, and the luster of an injection-moldedarticle is liable to vary within a molded article. In contrast, when theluster is too large, the impact resistance tends to be reduced. By theterm “vinyl bond content” herein used is meant both of the content of1,2-vinyl bond and the content of 3,4-vinyl bond in the conjugated dienemonomer units. Either or both of 1,2-vinyl bond and 3,4-vinyl bond maybe present in the conjugated diene monomer units.

Aromatic vinyl monomers used for the production of the above-mentionedblock copolymer rubber include, for example, styrene, 2-methylstyrene,3-methylstyrene, 4-methylstyrene, 2,4-diisopropylstyrene,2,4-dimethylstyrene, 4-t-butylstyrene and 5-t-butyl-2-methylstyrene. Ofthese, styrene is preferable.

The content of the aromatic vinyl monomer units in the block copolymerrubber is such that the lower limit thereof Is 25% by weight, preferably27% by weight and more preferably 35% by weight, and the upper limitthereof is 50% and preferably 45% by weight. When the content of thearomatic vinyl monomer units is too small, the luster is poor. Incontrast, when the content of aromatic vinyl monomer units is too large,the impact resistance is poor.

The ratio of blocked aromatic vinyl in the block copolymer rubber of thepresent invention of the present invention must be at least 70%, and ispreferably at least 75% and especially preferably at least 80%. With anincrease of the ratio of blocked aromatic vinyl, the luster becomesexcellent. If the ratio of blocked aromatic vinyl is lower than 70%, theluster Is reduced.

The ratio of blocked aromatic vinyl is measured by the osmium oxidativedegradation method described in I. M. Kolthoff et al, J. Polym. Sci., 1,429 (1948), and means the ratio in % of the amount of aromatic vinylmonomer units forming an aromatic vinyl monomer chain having a molecularweight of about 1,000 to the total amount of aromatic vinyl monomerunits.

The block copolymer rubber has a number average molecular weight suchthat the lower limit thereof is 280,000 and preferably 300,000, and theupper limit thereof is 1,000,000, preferably 800,000 and more preferably700,000. If the number average molecular weight is too small, the impactresistance is liable to be poor. In contrast, if the number averagemolecular weight is too large, the luster is liable to be poor.

The ratio (Mw/Mn) of weight average molecular weight (Mw) to numberaverage molecular weight (Mn) in the block copolymer rubber is in therange of about 1.02 to 2, preferably about 1.05 to 1.3.

The block copolymer rubber has a solution viscosity as measured on a 5%solution in styrene such that the lower limit thereof is preferably 20mPa·s and more preferably 23 mPa·s, and the upper limit thereof ispreferably 200 mPa·s, more preferably 100 mPa·s and especiallypreferably 70 mPa·s. If the solution viscosity is too small, the impactresistance is insufficient and the luster tends to be greatly reduced.In contrast, if the solution viscosity is too large, the luster isinsufficient and tends to vary within a shaped article.

The block copolymer rubber may contain monomer units other than theconjugated diene monomer units and the aromatic vinyl monomer units,provided that the effect of the invention is substantially obtained. Theamount of such optional monomer is preferably not larger than 40% byweight, more preferably not larger than 30% by weight and especiallypreferably not larger than 15% by weight. As specific examples of theoptional monomer, there can be mentioned non-conjugated diene monomerssuch as 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadieneand 5-ethylidene-2-norbornene; acrylic and methacrylic acid estermonomers such as methyl acrylate and methyl methacrylate; andα,β-ethylenically unsaturated nitrile monomers such as acrylonitrile,methacrylonitrile and α-chloroacrylonitrile.

Of the above-mentioned block copolymer rubbers, a block copolymer rubberhaving a block or blocks predominantly comprised of aromatic vinylmonomer units and a block or blocks predominantly comprised of butadieneunits are preferable, A block copolymer rubber having a single blockpredominantly comprised of styrene units and a single blockpredominantly comprised of butadiene units, namely, a styrene-butadienediblock copolymer rubber is especially preferable.

The process for producing the block copolymer rubber of the presentinvention is not particularly limited, and includes a process forpolymerizing an aromatic vinyl monomer and a conjugated diene monomer,for example, by using an organic active metal compound as initiator inthe presence of a polar compound such as a Lewis base in a hydrocarbonsolvent. This polymerization process preferably comprises (a) a step ofpolymerizing a conjugated diene monomer alone, and (b) a subsequent stepof polymerizing an aromatic vinyl monomer alone, and if desired, (c) astep of polymerizing a mixture of the conjugated diene monomer and thearomatic vinyl monomer, which intervenes, between the step (a) and thestep (b).

As specific examples of the hydrocarbon solvent, there can be mentionedaliphatic hydrocarbons such as butane, pentane and hexane; alicyclichydrocarbons such as cyclopentane and cyclohexane; and aromatichydrocarbons such as benzene, toluene and xylene. These hydrocarbonsolvents may be used either alone or as a combination of at least twothereof.

The organic active metal compound includes, for example, those which arecapable of being anion-polymerized, such as organic alkali metalcompounds and organic alkaline earth metal compounds. Of these, organicalkali metal compounds are preferable in view of high polymerizationreactivity and low material cost. As specific examples of the organicalkali metal compound, there can be mentioned monofunctionalorganolithium compounds such as n-butyllithium, sec-butyllithium,t-butyllithium, hexyllithium, phenyllithium and stilbenelithium;polyfunctional organolithium compounds such as dilithiomethane,1,4-dilithlobutane, 1,4-dilithio-2-ethylcyclohexane and1,3,5-trilithiobenzene; and sodium naphthalene and potassiumnaphthalene. Of the organic alkali metal compounds, organolithiumcompounds are preferable. Monofunctional organolithium compounds areespecially preferable. As specific examples of the organic alkalineearth metal compound, there can be mentioned n-butylmagnesium bromide,n-hexylmagnesium bromide, ethoxycalcium, calcium stearate,t-butoxystrontium, ethoxybarium, isopropoxybarium, ethylmercaptobarium,t-butoxybarium, phenoxybarium, diethylaminobarium, barium stearate andethylbarium. These organic active metal compounds may be used eitheralone or as a mixture of at least two thereof,

The amount of the organic active metal compound used is appropriatelychosen depending upon the desired molecular weight of the blockcopolymer rubber, but is in the range of about 0.1 to 10 m-mol andpreferably about 0.2 to 2 m-mol, per 100 g of the total monomers.

As specific examples of the polar compound, there can be mentionedethers such as tetrahydrofuran, diethyl, ether, dioxane, ethylene glycoldimethyl ether, ethylene glycol dibutyl ether, diethylene glycoldimethyl ether and diethylene glycol dibutyl ether; tertiary amines suchas tetramethylethylenediamine, trimethylamine, triethylamine, pyridineand quinuoridine; alkali metal alkoxides such as potassium t-amyloxideand potassium t-butoxide; and phosphines such as triphenylphosphine.These polar compounds may be used either alone or as a combination of atleast two thereof.

The amount of the polar compound used is appropriately chosen so as togive a block copolymer rubber having the desired vinyl bond content,although the amount thereof varies depending upon the kind of polarcompound and the polymerization temperature. For example, whentetamethylethylenediamine is used, its amount is in the range of about0.5 to 20 mol, preferably about 1 to 10 mol, per mol of an organicactive metal compound used as initiator. When the amount of the polarcompound is too small or too large, a block copolymer rubber having thedesired high vinyl bond content is difficult to obtain.

[Modifier for Resin]

The modifier for resin of the present invention comprises theabove-mentioned block copolymer rubber, and is useful as animpact-resistance modifier or a toughening agent. The modifier for resinmay contain other ingredients such as rubber other than theabove-mentioned block copolymer rubber, and additives conventionallyused In a resin industry, provided that the effect of the presentinvention can be substantially obtained.

As specific examples of the rubber other than the above-mentioned blockcopolymer rubber, there can be mentioned a conjugated diene polymerrubber represented by polybutadiene, and an aromatic vinyl-conjugateddiene copolymer rubber other than the above-mentioned block copolymerrubber. The additive includes, for example, mineral oil and liquidparaffin. When a resin-forming monomer such as styrene is polymerized inthe presence of the modifier for resin, the ingredient to beincorporated in the modifier for resin is preferably appropriatelychosen from those which give no baneful influence upon thepolymerization reaction.

[Resin Composition]

The resin composition of the present invention comprises 2 to 25% byweight of the above-mentioned block copolymer rubber and 98b to 75% byweight of a resin.

The resin used is not particularly limited, and includes, for example,general thermoplastic resins such as aromatic vinyl resins and olefinresins, engineering plastics, and thermoplastic resins. Of these,aromatic vinyl resins are preferably used.

As specific examples of the aromatic vinyl resins, there can bementioned an acrylonitrile-acrylate-styrene copolymer resin, anacrylonitrile-ethylene-styrene copolymer resin, an acrylonitrile-styrenecopolymer resin, an acrylonitrile-butadiene-styrene copolymer resin, apolystyrene resin, a high-impact polystyrene resin and a methylmethacrylate-styrene copolymer resin. Of these, a polystyrene resin isbeneficially used. As specific examples of the olefin resins, there canbe mentioned polyethylene and polypropylene. As examples of theengineering plastics, there can be mentioned polyphenylene ether,polyamide, polycarbonate, polyacetal and polyester. These resins may beused either alone or as a combination of at least two thereof.

The amount of the above-mentioned block copolymer rubber in the resincomposition of the present invention is such that the lower limitthereof is 2% by weight, preferably 3% by weight and especiallypreferably 5% by weight, and the upper limit thereof is 25% by weight,preferably 20% by weight and especially preferably 15% by weight. Theamount of the resin in the resin composition of the present invention issuch that the lower limit thereof is 75% by weight, preferably 80% byweight and especially preferably 85% by weight, and the upper limitthereof is 98% by weights preferably 97% by weight and especiallypreferably 95% by weight. If the amount of the block copolymer rubber istoo small, the impact resistance is poor. In contrast, if the amount ofthe block copolymer rubber is too large, the luster, rigidity, weatherresistance and hardness are liable to be poor.

If desired, ingredients conventionally used in a resin industry can beincorporated in the resin composition of the present invention. Theingredients include, for example, mineral oil, liquid paraffin, organicand inorganic fillers, a stabilizer, a plasticizer, a lubricant, anultraviolet absorber, a colorant, a release agent, an antistatic agentand a fire retardant. The amount of the ingredient used is appropriatelychosen within a range such that the effect of the present invention issubstantially obtained.

The process for producing the resin composition of the present inventionis not particularly limited. A resin and the block copolymer can bemechanically mixed together. Alternatively, a resin-forming monomer canbe polymerized in the presence of the block copolymer rubber. The latterprocess is preferable because a resin composition having excellentimpact resistance is easily obtained.

The method of mechanically mixing a resin with the block copolymer canbe carried out in a conventional manner by using a mixing or kneadingmeans such as a single or twin screw extruder, a Banbury mixer, a rollor a kneader. The mixing temperature is preferably in the range of 100to 250° C. In this mechanically mixing method, a thermoplastic resin isused.

In the method of polymerizing a resin-forming monomer in the presence ofthe block copolymer rubber, the block copolymer rubber is dissolved ordispersed in the resin-forming monomer to prepare a monomer liquid forpolymerization, and then, the monomer liquid is polymerized by anappropriate procedure such as bulk, suspension, solution or emulsionpolymerization procedure. Especially when an aromatic vinyl monomer ispolymerized in the presence of the block copolymer rubber, an aromaticvinyl resin composition having an excellent impact resistance can beobtained.

In the bulk polymerization procedure, the block copolymer rubber isdissolved or dispersed in a resin-forming monomer, and, if desired, amolecular weight modifier, a lubricant and other ingredient areincorporated in the solution or dispersion, and further, an initiator isadded therein to conduct a bulk polymerization in an inert gasatmosphere with stirring. When an aromatic vinyl monomer is polymerizedby the bulk polymerization procedure, the polymerization temperature ispreferably in the range of 60 to 200° C. In the suspensionpolymerization procedure, the block copolymer rubber is dissolved in aresin-forming monomer in a manner similar to the bulk polymerizationprocedure, and, if desired, a molecular weight modifier, a lubricant andother ingredient are incorporated and further an initiator is added inthe solution, and then, the solution is dispersed in an aqueous solutioncontaining a suspension stabilizer where a polymerization is carried outwhile a suspension state is maintained. After completion of thesuspension polymerization, the suspension stabilizer is thoroughlyremoved by washing with water to recover a resin composition. When anaromatic vinyl monomer is polymerized by the suspension polymerizationprocedure, the polymerization temperature is preferably in the range of60 to 150° C.

In the solution polymerization procedure, the block copolymer rubber isdissolved in a resin-forming monomer in a manner similar to the bulkpolymerization procedure, and, if desired, a molecular weight modifier,a lubricant, an organic solvent for viscosity control and otheringredient are incorporated and further an initiator is added in thesolution to conduct a polymerization in an inert gas atmosphere withstirring. When an aromatic vinyl monomer is polymerized by the solutionpolymerization procedure, the polymerization temperature is preferablyin the range of 60 to 200° C. A two stage polymerization procedure canbe employed wherein a bulk polymerization is carried out in the firststage until 10 to 50% by weight of a resin-forming monomer ispolymerized, and then, a suspension or solution polymerization iscarried out in the second stage.

The resin composition of the present invention is preferablythermoplastic, and preferably has a melt flow rate of at least 0.1 g/10min, more preferably 0.5 to 20 g/10 min as measured at 200° C. under aload of 5 kg according to JIS K6871. If the melt flow rate is too smallor too large, kneading becomes difficult and the dispersion of blockcopolymer rubber in the resin becomes non-uniform, and thus, themodifying effect of the present invention tends to be insufficient.

The invention will now be described more specifically by the followingexamples and comparative examples.

The physical properties were evaluated by the following methods.

(1) Number Average Molecular Weight (Mn) of Block Copolymer Rubber

Mn of a block copolymer rubber was measured by gel permeationchromatography using tetrahydrofuran as solvent and expressed in termsof that of standard polystyrene. A high performance liquid chromatograph“HLC-8020” available from Tosoh Corporation was used. The column usedwas “G4000HXL” and “G5000HXL” (both are available from TosohCorporation) which were connected in series).

(2) Content of Styrene units and Content of Vinyl Bond in ButadieneUnits

These contents were measured by a infrared spectrophotometer accordingto the Hampton method [R. Hampton, Anal. Chem., 21, 923(1949)].

(3) Ratio of Blocked Styrene

The ratio of blocked styrene was measured by the osmium oxidativedegradation method described in I. M. Kolthoff et al, J. Polym. Sci., 1,429 (1948). That is, 0.05 g of a block copolymer rubber was dissolved in10-ml of carbon tetrachloride, and then, 16 ml of an aqueous 70%solution of tert-butyl hydrperoxide and 4 ml of a 0.05% solution ofosmium tetraoxide in chloroform were added to the copolymer rubbersolution. The mixture was refluxed at 90° C. for 15 minutes to conductan oxidative degradation. The reaction mixture was cooled, and then, 200ml of methanol was added thereto with stirring to precipitate a blockedstyrene ingredient. The precipitate was filtered by a glass filterhaving pores with an average diameter of 5 μm. The filter cake wasweighed. The ratio of blocked styrene was expressed by the ratio in % ofthe weight thereof to the total weight of the styrene monomer units.

(4) Izod Impact Strength

A test specimen was prepared by injection molding using an injectionmolding machine “SAV-30/30” available from Yamashiro Seiki K. K., at amold temperature of 50° C. and a nozzle tip temperature of 240° C. Izodimpact strength was measured at 25° C. according to JIS K7110.

(5) Luster

A square specimen having a size of 9 cm×5 cm×2 mm (thickness) wasprepared by injection molding in the same manner as mentioned in (4).Luster was measured according to JIS Z8741 at an incidence angle of 60°.An injection port was located on a center straight line extending in thelongitudinal direction and 1 cm apart from one side of 5 cm. A moltenresin composition was injected through the injection port in a directionperpendicular to the major surface of specimen. Luster was measured ontwo points, i.e., in gate portion and end portion of theinjection-molded specimen. The measuring point in gate portion and themeasuring point in end portion were located on a center straight lineextending in the longitudinal direction on the injection port side and 2cm and 7 cm apart from the end of injection port side of specimen(namely, 1 cm and 6 cm apart from the injection port), respectively.

(6) Thermal Stability of Luster

Luster was measured on the specimen by the procedure mentioned in (5)according to JIS Z8741 before and after heat-treatment of the specimen.The thermal stability of luster was expressed by the ratio in % of theluster as measured after heat-treatment to the luster as measured beforeheat-treatment. The heat-treatment was carried out by placing a specimenon a stainless steel sheet covered with a polytetrafluoroethylene sheet,placing the assembly of specimen horizontally on a rotary disc in aforced hot air oven, and maintaining the specimen at 90° C. for 3 hoursin the oven.

EXAMPLE 1

The inner atmosphere of a stainless steel reaction vessel was replacedwith nitrogen, and the reaction vessel was charged with 7 kg ofpreviously purified cyclohexane, 8.57 mmol ofN,N,N′,N′-tetramethylethylenediamine and 600 g of 1,3-butadiene. Thecontent was heated to 50° C. and then 4.4 ml of a solution ofn-butyllithium (1.65 mmol/ml) in hexane was added to initiatepolymerization. Immediately after the commencement of polymerization,temperature was elevated to 60° C. at a rate of 0.5° C./min and thecontent was maintained at that temperature (first stage polymerization).When the polymerization conversion reached 100%, 400 g of styrene wasadded and the polymerization was continued. When the polymerizationconversion of styrene reached 100%, the reaction mixture was cooled to20° C. and 29.7 mmol of isopropyl alcohol was added to stop thepolymerization. Then 2 g of a phenolic antioxidant (“Irganox 1076”available from Ciba-Geigy AG) was added and the reaction mixture wasrecovered. The reaction mixture was subjected to steam stripping toremove the solvent and then, vacuum-dried to give styrene-butadienecopolymer rubber 1. The properties of the copolymer rubber 1 are shownin Table 1.

10 parts by weight of styrene-butadiene copolymer rubber 1 was dissolvedin 90 parts by weight of styrene monomer, and then 300 ppm of a chaintransfer agent (n-dodecyl mercaptan) was added to the solution ofcopolymer rubber 1 to prepare a styrene resin-forming monomer liquidformulation.

A 4-liter reaction vessel was charged with 2,300 g of the styreneresin-forming monomer liquid formulation. Polymerization was carried outat 130° C. with thorough stirring until the solid content reached 45% byweight.

The polymerization mixture was taken out from the reaction vessel andcooled to 20° C. to give 625 g of a polymerization liquid. A 4-literstainless steel reaction vessel was charged with 625 g of thepolymerization liquid and 1,875 g of an aqueous 0.5 weight % solution ofpolyvinyl alcohol (“Gosenol GH-20” available from Nippon Synthetic Chem.Ind. Co.) as a dispersant. The content was heated to 70° C. while beingstirred, and then, 1.25 g of benzoyl peroxide and 0.63 g of dicumylperoxide as radical polymerization initiators were added to the content.Suspension polymerization was carried out at 70° C. for 1 hour, at 90°C. for 1 hour, at 110° C. for 1 hour and further at 130° C. for 4 hours.After completion of the polymerization, the polymerization mixture wascooled to 20° C., and then filtered to recover a polymer. The recoveredpolymer was washed with water, dehydrated, and then, vacuum-dried at 60°C. for 12 hours to give polystyrene resin composition A.

Polystyrene resin composition A was milled by a roll mill at 180° C. toprepare a sheet. The sheet was pelletized into pellets by asheet-pelletizer. The pellets were injection-molded to prepare a testspecimen. Izod impact strength, luster and stability of luster weremeasured. The results are shown in Table 1.

EXAMPLE 2

The inner atmosphere of a stainless steel reaction vessel was replacedwith nitrogen, and the reaction vessel was charged with 7 kg ofpreviously purified cyclohexane, 8.57 mmol ofN,N,N′,N′-tetramethylethylenediamine and 400 g of 1,3-butadiene. Thecontent was heated to 50° C. and then 4.4 ml of a solution ofn-butyllithium (1.65 mmol/ml) in hexane was added to initiatepolymerization. Immediately after the commencement of polymerization,temperature was elevated to 60° C. at a rate of 0.5° C./min and thecontent was maintained at that temperature (first stage polymerization).When the polymerization conversion reached 100%, 200 g of 1,3-butadieneand 200 g of styrene were added and the polymerization was continued.When the polymerization conversion of the added 1,3-butadiene andstyrene reached 100%, the reaction mixture was cooled to 20° C., Thepolymerization mixture was treated by the same procedures as in Example1 to give styrene-butadiene copolymer rubber 2. The properties of thecopolymer rubber 2 are shown in Table 1.

By the same procedures as in Example 1, polystyrene resin composition Bwas prepared wherein styrene-butadiene copolymer rubber 2 was usedinstead of styrene-butadiene copolymer rubber 1 with all otherconditions remaining the same. The properties of polystyrene resincomposition B are shown in Table 1.

EXAMPLE 3

By the same procedures as in Example 1, styrene-butadiene copolymerrubber 3 was prepared wherein the amount ofN,N,N′,N′-tetramethylethylenediamine was changed to 4.15 mmol, theamount of butadiene was changed to 700 g and the amount of styrene waschanged to 300 g. All other conditions remained the same. The propertiesof the copolymer rubber 3 are shown in Table 1.

By the same procedures as in Example 1. polystyrene resin composition Cwas prepared wherein styrene-butadiene copolymer rubber 3 was usedinstead of styrene-butadiene copolymer rubber 1 with all otherconditions remaining the same. The properties of polystyrene resincomposition C are shown in Table 1.

TABLE 1 Example Comp. Example 1 2 3 1 2 Copolymer rubber 1 2 3 — 4Number average molecular 32 31 33 — 30 weight (×10,000) Viscosity of 5%styrene 26 24 25 — 33 solution (mPa · s) Content of 1,3-butadiene 60 6070 — 60 units (wt. %) Content of vinyl bond (wt. %) 71 72 56 — 10Content of styrene units 40 40 30 — 40 (wt. %) Ratio of blocked styrene(%) 98 81 98 — 98 Polystyrene resin composition A B C PS*₁ D Izod impactstrength (kJ/m²) 3.1 3.2 3.4 1.8 3.4 Luster at end portion (%) 94 94 93125 90 Luster at gate portion (%) 90 90 88 123 84 Luster at end portion93 93 91 124 87 after heat-treatment (%) Luster retention at end portion99 99 98 99 97 after heat-treatment (%) PS*₁: Polystyrene

Comparative Example 1

A styrene resin-forming monomer liquid formulation containing 300 ppm ofa chain transfer agent (n-dodecyl mercaptan) was prepared in the samemanner as in Example 1 wherein styrene-butadiene copolymer rubber 1 wasnot used. By the same procedures as in Example 1, suspensionpolymerization of the styrene resin-forming monomer liquid formulationwas carried out to give polystyrene resin. The properties of thepolystyrene resin are shown in Table 1.

Comparative Example 2

By the same procedures as in Example 1, styrene-butadiene copolymerrubber 4 was prepared wherein N,N,N′,N′-tetramethylethylenediamine wasnot used, and the amount of a solution of n-butyllithium (1.65 mmol/ml)in hexane was changed to 4.5 ml with all other conditions remaining thesame. The properties of the copolymer rubber 4 are shown in Table 1.

By the same procedures as in Example 1, polystyrene resin composition Dwas prepared wherein styrene-butadiene copolymer rubber 4 was usedinstead of styrene-butadiene copolymer rubber 1 with all otherconditions remaining the same. The properties of polystyrene resincomposition D are shown in Table 1.

As seen from the results shown in Table 1, the resin composition of thepresent invention has good impact resistance and thermal stability ofluster, and is characterized in that the luster varies only to aminimized extent within a shaped article. In contrast, polystyrene resinnot containing the styrene-butadiene block copolymer rubber as amodifier has very poor impact resistance (Comparative Example 1). Evenif a styrene-butadiene block copolymer rubber is used, when the contentof vinyl bond in butadiene units is too small, the luster isinsufficient, the reduction of luster after heat-treatment is greatlylarge, and an injection-molded article exhibits large variation inluster within the article (Comparative Example 2).

INDUSTRIAL APPLICABILITY

The resin composition of the present invention has good andwell-balanced impact resistance and luster, and is characterized in thatthe luster is thermally stable and the luster of an injection moldedarticle varies only to a minimized extent within the molded article.Therefore, the resin composition of the present invention is useful forelectric appliances, business machines, packaging containers,miscellaneous goods and other articles.

What is claimed is:
 1. An aromatic vinyl-conjugated diene blockcopolymer rubber comprising 50 to 75% by weight conjugated diene monomerunits and 25 to 50% by weight of aromatic vinyl monomer units, whereinthe content of vinyl bond in the conjugated diene monomer units is 55 to90% by weight, the ratio of blocked aromatic vinyl is at least 70% andthe number average molecular weight of the copolymer rubber is in therange of 280,000 to 1,000,000.
 2. The block copolymer rubber accordingto claim 1, which comprises 55 to 65% by weight of conjugated dienemonomer units and 35 to 45% by weight of aromatic vinyl monomer units.3. The block copolymer rubber according to claim 1, which has a solutionviscosity in the range of 20 to 200 cps as measured on a 5% solution instyrene.
 4. The block copolymer rubber according to claim 1, wherein theratio of blocked aromatic vinyl is at least 80%.
 5. The block copolymerrubber according to claim 1, wherein the conjugated diene monomer isbutadiene and the aromatic vinyl monomer is styrene.
 6. A modifier forresin which comprises a block copolymer rubber as claimed in claim
 1. 7.A resin composition comprising 2 to 25% by weight of a block copolymerrubber as claimed in claim 1, and 98 to 75% by weight of a resin.
 8. Theresin composition according to claim 7, wherein the resin isthermoplastic.
 9. The resin composition according to claim 8, whereinthe resin is an aromatic vinyl resin.
 10. A process for producing aresin composition characterized by polymerizing a monomer for forming aresin in the presence of a block copolymer rubber as claimed in claim 1.11. The process for producing a resin composition according to claim 10,wherein the monomer for forming a resin is an aromatic vinyl monomer.